(1) Field of the Invention
The present invention relates to an improved connection system for a vehicle wheel spokes.
(2) Description of the Related Art
Heretofore, the vast majority of bicycle wheels have been constructed using steel wire spokes that are connected, at their inner end, to a central hub component and, at their outer end, to a metallic rim hoop. The spokes are generally of steel construction while the hub and rim are commonly of aluminum or steel construction. The individual spokes, hub and rim are each formed as separate components that are then joined together with mechanical connections.
The manufacture of the hub component is an expensive process. Some hub shells are machined from aluminum billet while others are cast or forged and subsequently machined. This machining operation generally requires at least three machining setups: first the cylindrical portions of the hub are turned on lathe, second, the spoke holes in one hub flange are drilled in a rotary index operation, and third, the opposite hub flange is drilled in a separate rotary index operation as well. This multi-step machining process adds considerable expense to the manufacture of the hub shell component.
The tensile forces within the spoke create relatively high stresses at their connection points and these connection points must therefore be capable of withstanding these stresses. In the conventional spoke connection arrangement, stresses due to the spoke tension are concentrated over a relatively small region of the hub flange, namely the portion of the hub flange material that is radially outward from the spoke hole. This requires that the hub flange construction be based on expensive, higher strength materials and the use of more expensive forming processes, such as forging, rather than less costly processes, such as die casting or injection molding. Further, these stresses require that the flange be designed with robust thickness, thus adding weight to the wheel assembly.
The spokes of most conventional wheels are constructed of steel wire with a sharp “J” bend close to the headed end and adjacent to the point where they pass through the hole in the flange. The “J” bend region of the spoke is considerably weaker and less ductile due to the overstress of the material to achieve this bend. As would be expected, the “J” bend region is a common breakage point for spokes of conventional design. Spoke manufacturers have attempted to compensate for this shortcoming by thickening the wire in this region, but this solution results in considerable extra expense and weight.
With conventional wheels, the spoke is simply passed through the flange hole until the head of the spoke contacts the edge of this hole. The result is a loose clearance fit between the hub flange and the spoke, which permits the spoke to squirm and shift inside this hole. This undesirable movement results in wear at the flange and additional flex at the rim and also causes the wheel to come out of alignment (true) rather easily.
Due to fabrication methods employed in conventional hub construction, it is very difficult to machine or otherwise create the details required to insure that the geometry of the hub flange conform to the spoke surface without any clearances. Such clearances allow flexure or movement under tensile loading of the spoke. Further, it is common practice for the builder of conventional wheels to manually bend the spokes in an attempt to conform the spoke to the hub flange and align the spoke in its direction toward the rim. This is obviously a compromise since, particularly in the case of bicycle wheels, the rim is of relatively light construction and any inconsistency in spoke tension or spoke flexure characteristics will cause the wheel to go out of true, or worse, will cause spoke breakage. When the tensile loads are not evenly shared by all of the spokes, the spokes with greater stresses will be more prone to breakage as will the portions of the rim and hub flange associated with these spokes.
In recent years, some attempt has been made to improve on this conventional wheel design, but the changes have been minor and still retain the same materials and basic configuration. Interestingly, many of these more modern designs are simply a rehash of inventions that are more than 80 years old. This is likely due to the fact that, aside from some more esoteric examples, these modern wheels rely on similar materials and construction techniques as those employed 80 years ago.
While there have been limited attempts to utilize fiber reinforced composite materials in the construction of the spoke, rim, and/or hub components, the processes involved in their manufacture are extremely labor-intensive, with many manual operations to lay up and bond the materials and components together. Further, since the construction involves thermoset molding and bonding techniques, which utilize extended curing and molding cycle times, multiple sets of molds and tools must be utilized in order to achieve reasonable production volumes. Thus, a high tooling expense is also required.
Accordingly, it is an objective of the present invention to overcome the forgoing disadvantages and provide an improved vehicle wheel with improved spoke attachment.